Carrier current system



Patented Feb. 27, 1940 UNITED STATES CARRIER CURRENT SYSTEM John L. Woodworth, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application December 19, 1935, Serial No. 55,277

. I '7 Claims. My invention relates to carrier current systems, and more particularly to systems of the type wherein high frequency currents are impressed on power current conductors for signal 5 or control purposes.

In the systems usually employed for the above purpose the high frequency currents utilized for signal or control purposes are impressed on the various feeder circuits connected to the commercial current carrying bus conductors of a subestation or generating station. Various load circuits are connected to each of the feeder circuits for dispensing power supplied to. the bus conductors by a suitable'commercial current genthereby reducing the efiiciency of the high frequency signaling or control system. It has further been found that the high frequency voltage drop across the equivalent impedance between 30, the bus conductors may cause undesired control operations to be effected by high frequency receivers connected to feeder circuits other than those upon which the high frequency voltage is directly impressed.

It is an object of my invention to overcome the above dimculties by providing a system wherein the power current apparatus connected at various points to the system network has substantially no effect'on the desired operation of the high fre- 40 quency. current circuits.

It is a further and more specific object of my invention to provide a system of the above type wherein the high frequency oscillations are impressed on the feeder circuits of the system in 45 such a manner as to maintain at a minimum value the high frequency voltage developed between the main bus conductors.

. It is an additional object of my invention toprovide in a system of the above character means 5 for preventing the load circuits connected to the selected feeder circuit upon which high frequency oscillations are impressed from affecting the operation of the high frequency current apparatus connected to the transmission system network.

,55 v In accordance with my invention I attain the above objects by providing current transformers for impressing the high frequency oscillations on the selected feeder. circuits and by connecting the current transformers in such manner that the high frequency voltage impressed on the bus con- 5 ductors by one-half of the selected feeder cirv cuits is substantially equal in magnitude and opposite in phase to the high frequency voltage impressed on the bus conductors by the other half of said selected feeder circuits.

Further, in accordance with my invention a circuit is provided in shunt with each of the commercial load circuits having the proper reactance at the high frequency to form a parallel resonant circuit with the reactance of the associated load circuit. With each of the load circuits converted into a resonant circuit in this manner the high frequency current drawn by each of the resonant networks is reduced to a very small value which is in phase with the high frequency voltage applied to the'associated feeder. With the above described circuit arrangement the high frequency current flowing in the bus conductors and the inactive feeder conductors, which current consists of the Vector sum of the currents in the several selected .feeders connected to the bus conductors, is reduced substantiallyto Zero, and hence the voltage drop between the bus conductors is decreased to a negligible value. This of course means that a greater h gh frequency voltage is available at. the terminals of the high frequency receivers connected to the selected feeder circuits upon which the high frequency voltage is impressed and that substantially no high frequency voltage is applied to the high frequency receivers connected to the unselected feeder circuits upon which no high frequency voltage is impressed.

The novel features which I believe to be characteristic of my invention are set forth with par- 40 ticularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing in which Fig. 1 illustrates a system having the features of my invention embodied therein, and Fig. 2. illustrates a portion of the system shown in Fig. l.

Referring to Fig. 1 of the drawing I have illustrated'ther'ein a system which comprises a power current source I connected to supply through a circuit breakerZ and a step-down transformer 3 commercial frequency current to a main bus 4 and 35.

comprising the conductors 5 and 6. A plurality of feeder circuits 'l8, 9-l0, l|l2, [3-44 and iE-lfi may be connected to the main bus conductors 5 and 6 in the manner illustrated. In addition, a step-down transformer I? may be connected to the bus 43 for conducting power to a utilizing circuit (not shown) as, for example, to a circuit for dispensing power in the generating or sub-station in which the bus 4 is located.

Each of the several feeder circuits may be connected at various points to commercial current utilizing circuits in any desired manner. A transformer coupling between the feeder circuit and each of the utilizing circuits, for changing the voltage ratio between the two circuits, is usually employed for this purpose, and I have indicated by way of illustration such coupling transformers l8, l9 and 20 as being connected respectively to the feeder circuits l-8, 9l0 and Iii-46. It will of course be understood that additional cou' pling transformers may be connected at various points along the feeder circuit 'I8 and, further, that each of the other feeder circuits illustrated may be coupled to power utilizing circuits in the same manner.

Connected in parallel with each of the utilizing circuits are shunt circuits which neutralize the effect of the impedance of the utilizing circuits on the highfrequency apparatus. Each of these shunt circuits includes a condenser 2| and an inductance 22 connected in series, the reactance values of the elements being selected in accordance with the principles described in detail hereinafter.

The high frequency transmitting system is shown as comprising a source of high frequency oscillations 23 connected to impress a high frequency voltage on bus conductors 24 and 25 through a circuit breaker 26 and a keying device 2'1. 32 are employed to impress the high frequency oscillations on the respective feeder circuits !-8 to I5--l6 inclusive. Alternate transformers are connected to the high frequency bus with their windings oppositely poled. Thus the transformers 28, 3! and 32 are connected to impress on the feeder circuits '!8, lI-l2 and |5-|6, oscillations which are in opposed phase relation to the oscillations impressed on the feeder cir-.

cuits 9l0 and I3-M by the transformers 29 The purpose of connecting the current transformers in this manner is set forth in detail hereinafter. Feeder selecting switches 33, 34 and 35 may be connected in the circuit leads between the transformers and the bus conductors'ze and 25 for the purpose of selecting the desired feeders on which the high frequency signal or control oscillations are to be impressed. Each of the high frequency circuits connected to the bus 26, 25 includes a blocking condenser 3'! for preventing the voltage of the power source I from being impressed on the bus conductors 24 and 25 and a phase correcting condenser 36 for obtaining substantially unity power factor between the voltage and current generated by the source 23.

Each of the several feeder circuits 18, to I5--l6 inclusive may have connected thereto one or more high frequency receiving systems for utilizing the high frequency currents to effect the desired control or signal operations. I have illustrated such a receiving system at 38 as being connected to the feeder circuit 1-8 through a pair of blocking condensers 39 and m. Although any desired form. of receiving sys- Current transformers 28, 29, 30, 3| and equivalent impedance is formed.

tem may be employed, preferably this system is of the type shown and described, in my copending application Serial No. 23,847.

In the operation of the above-described system it will be understood that normally power currents of commercial frequency are supplied to the various load circuits connected to the conductors 5 and 6 of the bus 4 and to the load circuits connected to the-feeders 1-4 to lE-IG inclusive.

Control operations of the high frequency receiving systems may selectively be effected by closing the desired feeder circuit selecting switches 33 to 35 inclusive and manipulating the key 21 to impress on the selected feeder circuits high frequency oscillations of the correct duration and code arrangement. Thus, if it be desired to produce a response of receivers connected to the feeder circuits IL-8 and 9-H], the switch 33 will be closed and the remaining switches 34 and 35 left open. Following closure of the switch 33 the key 21 may beoperated to transmit the proper high frequency impulses to produce a response of the receivers connected to the feeder circuits 1-8 and 9-H].

With the above arrangement and when high frequency oscillations are being impressed only on a portion of the several feeder circuits the load impedances connected to the remaining or inactive feeder circuits, and the impedance of the power apparatus elements connected across the bus conductors '5 and 6, such, for example,

as the elements 3 and i1, may each draw relatively large high frequency currents. The high frequency voltage drop produced by these currents across the several impedances formed by the power apparatus elements tends to reduce the high frequency voltage available for producing a response in the high frequency receivers connected to the selected feeders. Further, this voltage drop being connected across the feeder circuits upon which no high frequency oscillations'are directly impressed may in certain cases be of sufiicient magnitude to effect an undesired operation of the high frequency receivers connected to these feeder circuits.

The above-described effect of large high frequency currents in the load impedances to reduce the efiiciency of the high frequency system will more clearly be understood by reference to Fig, 2 which shows only a portion of the transmission system illustrated in Fig. 1. In the circuit illustrated in Fig. 2 high frequency oscillations are impressed only on the feeder circuits l'8 and 9il. With this circuit arrangement the load impedances connected to the inactive feeder circuits lll2 to l5-l6 inclusive, upon which no high frequency oscillations are impressed, and the impedance of the power app a ratus elements connected to the bus conductors 5 and 6, are in parallel and may be combined to form a single equivalent impedance as indicated in dotted lines at M. It will 'be noted that this equivalent impedance is connected across each of the impedances from which the It will further be seen that if the high frequency oscillationsare impressed on the feeder circuits 1-8 and 8-H] in such manner that the high frequency currents flowing in the conductors 5 and B are in phase, a high frequency voltage drop will be produced across the equivalent impedance 4| which must be subtracted from the impressed. high frequency voltage to obtain the high fre-, quency voltage existing at the terminals of the'75- receiver 38 connected to the feeder circuit 1-8. The high frequency voltage drop across the impedance will of course be impressed on the inactive feeder circuits on which no high frequency oscillations are directly impressed, and may in certain cases be sufficient to cause undesired response of the high frequency receivers connected to these feeder circuits.

However, if the current flowing from the feeder conductor 8 into the bus conductor 5 be equal in magnitude and opposite in phase to the current flowing from the conductor 5 into the feeder conductor In, these currents will cancel in the equivalent impedance Al and no high frequency voltage drop will exist between the bus conductors 5 and 6, or between the conductors on the inactive feeder circuits connected to the bus conductors and upon which no high frequency oscillations are directly impressed.

'-,the two polarities.

In accordance with my invention equal and oppositely phased currents are obtained in the bus conductors EB and the equivalent impedance M by connecting the primary windings of the current transformers of the several pairs of feeder circuits in opposed phase relation and by providing the circuits 2|, 22 connected one in shunt with each of the commercial current load impedances connected to the several feeder circults.

Thus, the current transformers 28 and 29 are shown as having their primary windings permanently connected together in reversed phase relation. In like manner the current transformers .30 and 3| have their primary windings connected in reversed phase relation. It will be understood that any additional pairs of feeder circuits connected to the bus conductors 5 and 6 will have'their current transformers connected in the same manner. If the number of feeder circuits is odd the extra feeder circuit may have its current transformer primary winding connected to the bus conductors 5, 6 with either of With the current transformers connected in this manner the high frequency voltages impressed on any pair of feeder circuits are displaced in phase by 130 degrees and if the impedances of the two circuits are {equal the currents flowing in the feeder and bus conductors will be displaced in phase by the same angle. Inequality in the 'impedances of the two circuits causes an inequality in the magnitude of the two currents and a phase displacement less than 180 degrees. This of course means that the Vector sum of the currents in the bus con- 55. ductors 5 and 6 will not equal zero and that a high frequency voltage will existbetween these conductors.

The magnitude of the high frequency current flowing in each of the several feeder circuits is the high frequency of the load impedances connected thereto. Similarly the phase relation which this current bears to the impressed volt age is also determined in part by the phase angles of these load in'ipedanoes. Thus, it will be seen that the magnitudes of the currents flowing from \the circuits 'lil and 9-9 0 through the equivalent impedance 4| are partially, determined by the values of the commercial load impedances connected to the respective feeders. If the, reactance values of these load impedances are equal at the high frequency, the currents flowing from the two feeder circuits through the equivalent impedance M will be equal in magnitude and opposite in phase and, accordingly, will combine to produce substantially no high frequency voltage drop across the equivalent impedance 4|. of course, is the desired operating condition.

Usually the commercial current load impedances connected to the selected feeder circuits on which high frequency oscillations are directly impressed are such that the high frequency reactances thereof are unequal. This means that the currents which passfrom these selected circuits through the equivalent impedance 4| will not be equal and will not bear the correct degrees phase displacement necessary for their cancellation. Accordingly, it is desirable to neutralize the effect of each of the several load impedances so that the high frequency currents fiowingin the feeder circuits are unaffected either in magnitude or phase by the commercial load impedances connected to the feeder circuits.

In accordance With my invention this is accomplished by providing the circuits 2|, 22 connected one in shunt to each of the load impedances and so proportioned in reactance that at the high frequency a parallel resonant circuit is formed across the line by the combined reactance of the shunted load impedance and that of the shunt circuit 2|, 22. Thus, in Fig. 2 if the series circuit 2|, 22 connected in shunt with the load impedance it be of such a reactance value that a parallel resonant circuit, is formed across the conductors '|& at the operating high frequency, only a negligible high frequency current will be drawn from the feeder circuit by the resonant circuit thus formed. In like manner the reactance values at the high frequency of the circuit 2|, 22 connected in parallel with the load impedance |9 may be so proportioned as to form a parallel resonant circuit with the impedance l9; which parallel resonant circuitis connected .minimize the effect of the load impedances connected to the feeder circuits on the phase and magnitude of the high frequency current flowing in the several feeder circuits. Since the transformers 28 to 32 inclusive, are connected to the several feeders with polarities such that the currents produced in the respective feeders tend to combine to produce a minimum high frequency current in the bus conductors 55, and the equivalent impedance 4H connected thereacross, it will be seen that by removing the effect of the several load impedances on the phase and magnitude of the high frequency currents in the manner described above, high frequency currents are enabled to combine inthe desired manner thereby to produce substantially no high frequency voltage drop between the bus conductors 5-6. Thus, if theload impedances l8 and is connected to the feeder circuits l'8 and 9--||l have substantially no effect onfthe phase and magnitude of current flowing in these two feeder circuits, they will be substantially equal in magnitude and will combine in the equivalent impedance 4% in opposed phase relation thereby to produce substantially no high frequency voltage drop across the equivalent impedance t i.

It will be understood that the nature of the reactance of each of the circuits 2|, 22 at the high frequency, 1. e. whether capacitive or inductive, will be determined by the nature of the re- This, a

actance of the load which the circuit shunts. Thus, with an inductive load impedance as indicated at It the reactance between the terminals ofthe circuit 2!, 22. connected thereacross at the high frequency must be capacitive and must be equal to the inductive reactance ofthe element 88, if a parallel resonant circuit is to be formed across the feeder circuit l8.. The purpose of employing the inductance 22 in the circuit is to eliminate the necessity of using a large and expensive condenser having-the physical characteristics necessary to withstand the high commercial voltage between the feeder conductors 1-8. Obviously, if one of the shunt circuits were employed to form a resonant circuit with a power factor correction condenser having a capacitive reactance at the high frequency, the reactance between the terminals of the shunt circuit at the high frequency would necessarily have to be inductive.

From the foregoing description of the circuits 2|, 22 it will be understood that they serve an additional purpose in the high frequency systern, viz. that of reducing the line voltage drop between the impressed high frequency voltage and the high frequency receivers. It will, therefore, be understood that the circuits 2!, 22 are not limited in their use to the particular type of high frequency transmisison system disclosed, and that they may be used in any system wherein it is desirable to reduce to a minimum the line drop between the impressed high frequency voltage and the high frequency receivers.

It is possible so to proportion the values of 1 reactance of the elements 2|, 22 at the high frequency that the resultant reactance due to the combined effect of the shunted impedance and the shunting circuit 2|, 22 is capacitive, in which case a rise in the voltage at the point of connection of the load impedance to the feeder circuit occurs. In the extreme case where resonance between the reactance of the circuit M, '22, the shunted load reactance, and the feeder line reactance is obtained, the voltage across the series circuit 2!, 22 may be many times the voltageimpressed on the feeder circuit. This is not desirable since it may produce failures in the insulation of the commercial current apparatus.

It has been found that by making the inductance 22 in the form of a saturable iron core reactor such resonance may be prevented and the voltage rise limited to any predetermined value by the current saturation of the core of the reactor. This will more clearly be understood when it is realized that as the current through the winding of the reactor increases, the core thereof saturates, thereby to reduce the inductance of the reactor and to increase the effective capacity between the terminals of the series cira smaller capacitor.

vIn a system such as that disclosed by Fig. there is the danger that when the high frequency oscillations are impressed upon one feeder circuit for the purpose of'operating the high frequency responsive apparatus thereon, there will be enough high frequency current finding its way from the one feeder circuit into some other feeder circuit by way of the bus-bar connections to produce an undesired actuation of the high frequency apparatus in that other feeder circuit. For example, if the high frequency oscillations are applied to the feeder circuit 1, 8 for the purpose of actuating the responsive device 38 connected therewith there may be enough high frequency voltage reaching the feeder cir-,

cuit l5, It by way of the bus-bars 5, 6 and transformers 3 or I! to cause an undesired actuation of the responsive device 38 applied to the feeder circuit I5, Hi. The possibility of such an undesired actuation is prevented or greatly reduced by the shunt circuit, including the reactance members 2!, 22 arranged across the primary of the transformer l8 which is the load impedance. This shunt circuit is so constructed that its reactance is opposite in character to that of the load impedance whereby the current passing the shunt circuit is in opposite phase relation to that which passes the primary of the transformer H8. The shunt circuit and the primary thus form a resonant circuit. It is well known that the impedance offered by such a circuit to the high frequencies in the feeder circuit is very high, in fact, if the inductive and capacitive reactances of the resonant circuit are exactly equal and if there were no resistance in the circuit the impedance would be infinite. resonant circuit on the feeder therefore is substantially that of an open circuit as far as the high frequencies are concerned. Such being the case there will be little or no high frequency cur rent flow in the feeder circuit I, 8 due to the load impedance thereof, hence that part of the high frequency impressed upon the feeder F, 8 which finds its way into the feeder i5, I5 is reduced to a very low value, if not entirely eliminated.

While in the preferred embodiment of my improved high fr-equency transmission system both the neutralizing circuits 2!, 22 and the reversed current transformer connections are employed, it

will be understood that in certain cases the neutween the primary windings of the current transformers are not essential, although they are advantageous in that they eliminate the possibility of impressing the high frequency oscillations on the selected feeder circuits in thewrong phase relation. However, a feeder circuit selecting device may be employed whereby any pair or pairs of feeder circuits may be connected to the bus The effect of the conductors 2425 in opposed phase relation for proper high frequency energization.

Although I have illustrated my invention as being applied to a single phase power transmission system, it will be readily understood by those skilled in the art that the invention may be ap-- plied to polyphase transmission systems as well. It will further be understood that my invention is not limited to the use of interrupted carrier oscillations for performing the desired control or signal operations. Thus, the high frequency oscillations generated by the source may be modulated with signal oscillations in any desired manthat I do not wish to be limited thereto-since whereby a rise in voltage occurs on said feeder many modifications in the circuit may be made, and I contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is 1 1. In a carrier current system, a feeder circuit for carrying currents of commercial and high frequencies, a source of high frequency oscillations, means for impressing said oscillations on said circuit toproduce a high frequency current in said circuit, a commercial load imcuit for carrying currents of commercial and I high frequencies, a source of high frequency oscillations, means for impressing said oscillations on said circuit to produce a high frequency current in said circuit, a commercial load impedance connected to said circuit, and a circuit including a series connected condenser and inductance connected in shunt to said load impedance and constructed to pass a high frequency reactive current opposite in phase and substantially equal to the high frequency reactive current passed by said load impedance;

3. In a carrier current system, a feeder circuit for carrying currents of commercial and high frequencies, a source of high frequency oscillations, means for impressing said oscillations on said circuit to produce a high frequency current in said circuit, a commercial load impedance connected to said circuit, a circuit including a condenser connected in shunt to said load impedance for controlling the magnitude of high frequency current flowing through said impedance from said feeder circuit and the high frequency voltage developed across said load impedance, and means including a saturable core reactor connected in said shunt circuit for automatically varying the high frequency current in said shunt circuit in accordance with the variations in the high frequency reactive current in the load impedance. I i

4. In a carrier current system, a feeder circuit for carrying currents of commercial andhigh frequencies, a source of high frequency oscillations, means for impressing said oscillations on said circuit to produce ahigh frequency current in said circuit, a commercial load impedance connected to said circuit, and a circuit including a series connected condenser and a saturable core reactor connected in shunt with said load impedance, the, combined effect of said load impedance and said shunt circuit being capacitive circuit at the point of connection therewith of said load impedance and said reactor, by saturating, serves to limit said rise in voltage.

5. In a carrier current system, bus conductors for carrying currents of commercial and high frequencies, an impedance connected across said conductors, a pluralityof feeder circuits connected to said bus conductors, a source of high" frequency oscillations, means for impressing said oscillations in oneof said feeder circuits, a load impedance connected to said one feeder circuit, high frequency responsive apparatus connected to each of said feeder circuits and,

means for reducing the effect of the oscillations impressed on said one feeder circuit on the high frequency responsive apparatus in another of said feeder circuits, said means comprising a circuit in shunt with said load impedance and including reactance constructed to pass high frequency reactive current opposite in phase tothehigh frequency reactive current passed by the load impedance. I 1

6. In a carrier current system, bus conductors for carrying currents of commercial and high frequencies, an impedance connected across said conductors, a plurality of feeder circuits connected to said bus conductors, a source of high frequency oscillations, means for selectively impressing said oscillations" in said feeder circuits, load impedances-and high frequency responsive apparatus connected to said feeder circuits, and means for reducing the effect in one feeder circuit of the oscillations impressed on another feeder circuit, said means comprising a circuit in shunt with the load impedance of said other feeder circuit and including reactance con-- v structed to pass high frequency reactive current opposite in phase to the high frequency reactive current passed by said load impedance.

'7. In a carrier current system, bus conductors for carrying currents of commercial and high frequencies, an impedance connected across said conductors, a plurality ,of feeder circuits connected to said bus conductors, a source of high frequency oscillations, means for selectively impressing said oscillations in said feeder circuits, load impedances and high frequency responsive apparatus connected to said feeder circuits, means for reducing the effect in one feeder circuit of the oscillations impressed on another feeder circuit, said means comprising a circuit in shunt withthe load impedance of said other feeder circuit and including reactance constructed to pass high frequency reactive current opposite in phase and substantially equal to the high frequency reactive currentzpassed by said load impedance, said shunt circuit including a saturable core reactor by whichcompensation is made for variations in said load impedance due to changes in the load.

' JOHN L. WOODWORTI-I. 

